The invention pertains to pressure sensing transducers utilizing a bellows and electric sliding contacts to selectively vary an electrical resistance in accord with the pressure sensed.
Pressure sensing transducers basically employ pressure sensing means capable of producing mechanical movement under the influence of the pressure being sensed, and this mechanical movement is converted into electric signals. Typical transducer devices employ bellows, Bourdon tubes, diaphragms, bimetal elements and other structure to sense the pressure while piezoelectric crystals, mercury and reed switches, potentiometers and other sliding contact resistance elements have been used to sense and indicate the movement of the pressure sensing device and convert such mechanical movement into an electric signal.
One sensitive transducer utilized to sense fluctuations, such as atmospheric, gas and fluid pressures, employs a flexible wall bellows, usually evacuated, which changes length in accord with the degree of pressure imposed upon the bellows by the surrounding medium. The condition of the bellows, i.e., the length thereof, is sensed by a sliding contact type device which is capable of varying its electrical resistance in accord with the relative condition of the bellows. For instance, the bellows may be connected to a potentiometer type device which varies resistance in accord with the position of the tap and the length of the resistance wire utilized in the circuit for a given potentiometer setting.
Transducer devices of the prior art utilizing sliding contacts have, in the past, employed motion magnification means between the switch contacts and the bellows in order to amplify the switch contact movement. Such amplification means commonly take the form of fulcrumed lever devices wherein a small movement of the bellows results in a considerably greater movement of the contact of the switch over the electric resistance member. Such devices have the disadvantage of inaccuracies due to the multiplication of movement, and wear and manufacturing tolerances in the moving parts. Further, such devices are relatively complex and expensive to manufacture, and are relatively bulky in size due to the plurality of components required. In the past, a direct connection between the bellows and the sliding contacts in a low tolerance transducer was not considered practical in view of the relatively limited bellows movement and the difficulty in orienting, calibrating and maintaining the desired relationships between the sliding contacts driven by the bellows and the resistance elements over which the contacts moved.